Inside Jennifer Aniston's Engagement to Justin Theroux

By Julie Jordan

08/15/2012 at 08:00 AM EDT

Jennifer Aniston and Justin Theroux hopped a private jet to New York City last weekend to celebrate Theroux's 41st birthday – but he had a little something else up his sleeve: an engagement ring.

On Aug. 10, Theroux's birthday, the pair of 15 months sat side by side at a corner table at Blue Hill restaurant in Manhattan, enjoying a quiet dinner and looking "like a long-term couple in love," a source tells PEOPLE in its new issue.

But the celebration was just getting started. As his rep exclusively revealed to PEOPLE, Theroux proposed that day – and Aniston, 43, gave him "an extraordinary gift" by accepting. "He's been dying to do it," says a Theroux pal of his popping the question. "His friends knew it was coming."

Immediately after Aniston's heartfelt "yes!" the couple called their families – including her father, actor John Aniston – and close pals to share the good news.

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"Everyone is really excited for them," adds a source. "It's amazing to see how happy Justin makes Jen, and everyone was always hoping that he would propose."

Friends say that the couple got serious about each other fast, and that actor-screenwriter Theroux is a perfect match for the laid-back Aniston. "They have the same low-key attitude about life," says a member of their inner circle. "They just click and complement each other."

For further details on Theroux's proposal to Aniston, including more on Aniston's joy, their families' reactions and the latest on wedding plans, pick up this week's issue of PEOPLE, on newsstands Friday

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